/*
 * This class if from google Guava project.
 * <dependency>
 *    <groupId>com.google.guava</groupId>
 *    <artifactId>guava-jdk5</artifactId>
 *    <version>17.0</version>
 * </dependency>
 */

/*
 * Copyright (C) 2011 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the
 * License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
 * express or implied. See the License for the specific language governing permissions and
 * limitations under the License.
 */
package scouter.extlib.com.google.common.primitives;

import java.math.BigInteger;

/**
 * Static utility methods pertaining to {@code long} primitives that interpret values as
 * <i>unsigned</i> (that is, any negative value {@code x} is treated as the positive value
 * {@code 2^64 + x}). The methods for which signedness is not an issue are in Longs, as
 * well as signed versions of methods for which signedness is an issue.
 *
 * <p>In addition, this class provides several static methods for converting a {@code long} to a
 * {@code String} and a {@code String} to a {@code long} that treat the {@code long} as an unsigned
 * number.
 *
 * <p>Users of these utilities must be <i>extremely careful</i> not to mix up signed and unsigned
 * {@code long} values. When possible, it is recommended that the UnsignedLong wrapper
 * class be used, at a small efficiency penalty, to enforce the distinction in the type system.
 *
 * <p>See the Guava User Guide article on <a href=
 * "http://code.google.com/p/guava-libraries/wiki/PrimitivesExplained#Unsigned_support">
 * unsigned primitive utilities</a>.
 *
 * @author Louis Wasserman
 * @author Brian Milch
 * @author Colin Evans
 * @since 10.0
 */

public class UnsignedLongs {
    private UnsignedLongs() {}

    public static final long MAX_VALUE = -1L; // Equivalent to 2^64 - 1

    /**
     * A (self-inverse) bijection which converts the ordering on unsigned longs to the ordering on
     * longs, that is, {@code a <= b} as unsigned longs if and only if {@code flip(a) <= flip(b)}
     * as signed longs.
     */
    private static long flip(long a) {
        return a ^ Long.MIN_VALUE;
    }

    /**
     * Compares the two specified {@code long} values, treating them as unsigned values between
     * {@code 0} and {@code 2^64 - 1} inclusive.
     *
     * @param a the first unsigned {@code long} to compare
     * @param b the second unsigned {@code long} to compare
     * @return a negative value if {@code a} is less than {@code b}; a positive value if {@code a} is
     *         greater than {@code b}; or zero if they are equal
     */
    public static int compare(long a, long b) {
        return compareLongs(flip(a), flip(b));
    }

    /**
     * Compares the two specified {@code long} values. The sign of the value
     * returned is the same as that of {@code ((Long) a).compareTo(b)}.
     *
     * <p><b>Note:</b> projects using JDK 7 or later should use the equivalent
     * Long#compare method instead.
     *
     * @param a the first {@code long} to compare
     * @param b the second {@code long} to compare
     * @return a negative value if {@code a} is less than {@code b}; a positive
     *     value if {@code a} is greater than {@code b}; or zero if they are equal
     */
    public static int compareLongs(long a, long b) {
        return (a < b) ? -1 : ((a > b) ? 1 : 0);
    }

    /**
     * Returns the least value present in {@code array}, treating values as unsigned.
     *
     * @param array a <i>nonempty</i> array of unsigned {@code long} values
     * @return the value present in {@code array} that is less than or equal to every other value in
     *         the array according to {@link #compare}
     * @throws IllegalArgumentException if {@code array} is empty
     */
    public static long min(long... array) {
        if (array.length > 0 == false) throw new IllegalArgumentException();
        long min = flip(array[0]);
        for (int i = 1; i < array.length; i++) {
            long next = flip(array[i]);
            if (next < min) {
                min = next;
            }
        }
        return flip(min);
    }

    /**
     * Returns the greatest value present in {@code array}, treating values as unsigned.
     *
     * @param array a <i>nonempty</i> array of unsigned {@code long} values
     * @return the value present in {@code array} that is greater than or equal to every other value
     *         in the array according to {@link #compare}
     * @throws IllegalArgumentException if {@code array} is empty
     */
    public static long max(long... array) {
        if (array.length > 0 == false) throw new IllegalArgumentException();
        long max = flip(array[0]);
        for (int i = 1; i < array.length; i++) {
            long next = flip(array[i]);
            if (next > max) {
                max = next;
            }
        }
        return flip(max);
    }

    /**
     * Returns a string containing the supplied unsigned {@code long} values separated by
     * {@code separator}. For example, {@code join("-", 1, 2, 3)} returns the string {@code "1-2-3"}.
     *
     * @param separator the text that should appear between consecutive values in the resulting
     *        string (but not at the start or end)
     * @param array an array of unsigned {@code long} values, possibly empty
     */
    public static String join(String separator, long... array) {
        if (separator == null) throw new IllegalArgumentException();
        if (array.length == 0) {
            return "";
        }

        // For pre-sizing a builder, just get the right order of magnitude
        StringBuilder builder = new StringBuilder(array.length * 5);
        builder.append(toString(array[0]));
        for (int i = 1; i < array.length; i++) {
            builder.append(separator).append(toString(array[i]));
        }
        return builder.toString();
    }

    /**
     * Returns dividend / divisor, where the dividend and divisor are treated as unsigned 64-bit
     * quantities.
     *
     * @param dividend the dividend (numerator)
     * @param divisor the divisor (denominator)
     * @throws ArithmeticException if divisor is 0
     */
    public static long divide(long dividend, long divisor) {
        if (divisor < 0) { // i.e., divisor >= 2^63:
            if (compare(dividend, divisor) < 0) {
                return 0; // dividend < divisor
            } else {
                return 1; // dividend >= divisor
            }
        }

        // Optimization - use signed division if dividend < 2^63
        if (dividend >= 0) {
            return dividend / divisor;
        }

        /*
         * Otherwise, approximate the quotient, check, and correct if necessary. Our approximation is
         * guaranteed to be either exact or one less than the correct value. This follows from fact
         * that floor(floor(x)/i) == floor(x/i) for any real x and integer i != 0. The proof is not
         * quite trivial.
         */
        long quotient = ((dividend >>> 1) / divisor) << 1;
        long rem = dividend - quotient * divisor;
        return quotient + (compare(rem, divisor) >= 0 ? 1 : 0);
    }

    /**
     * Returns dividend % divisor, where the dividend and divisor are treated as unsigned 64-bit
     * quantities.
     *
     * @param dividend the dividend (numerator)
     * @param divisor the divisor (denominator)
     * @throws ArithmeticException if divisor is 0
     * @since 11.0
     */
    public static long remainder(long dividend, long divisor) {
        if (divisor < 0) { // i.e., divisor >= 2^63:
            if (compare(dividend, divisor) < 0) {
                return dividend; // dividend < divisor
            } else {
                return dividend - divisor; // dividend >= divisor
            }
        }

        // Optimization - use signed modulus if dividend < 2^63
        if (dividend >= 0) {
            return dividend % divisor;
        }

        /*
         * Otherwise, approximate the quotient, check, and correct if necessary. Our approximation is
         * guaranteed to be either exact or one less than the correct value. This follows from fact
         * that floor(floor(x)/i) == floor(x/i) for any real x and integer i != 0. The proof is not
         * quite trivial.
         */
        long quotient = ((dividend >>> 1) / divisor) << 1;
        long rem = dividend - quotient * divisor;
        return rem - (compare(rem, divisor) >= 0 ? divisor : 0);
    }

    /**
     * Returns the unsigned {@code long} value represented by the given decimal string.
     *
     * @throws NumberFormatException if the string does not contain a valid unsigned {@code long}
     *         value
     * @throws NullPointerException if {@code s} is null
     *         (in contrast to {@link Long#parseLong(String)})
     */
    public static long parseUnsignedLong(String s) {
        return parseUnsignedLong(s, 10);
    }

    /**
     * Returns the unsigned {@code long} value represented by a string with the given radix.
     *
     * @param s the string containing the unsigned {@code long} representation to be parsed.
     * @param radix the radix to use while parsing {@code s}
     * @throws NumberFormatException if the string does not contain a valid unsigned {@code long}
     *         with the given radix, or if {@code radix} is not between {@link Character#MIN_RADIX}
     *         and {@link Character#MAX_RADIX}.
     * @throws NullPointerException if {@code s} is null
     *         (in contrast to {@link Long#parseLong(String)})
     */
    public static long parseUnsignedLong(String s, int radix) {
        if (s == null) throw new IllegalArgumentException();
        if (s.length() == 0) {
            throw new NumberFormatException("empty string");
        }
        if (radix < Character.MIN_RADIX || radix > Character.MAX_RADIX) {
            throw new NumberFormatException("illegal radix: " + radix);
        }

        int max_safe_pos = maxSafeDigits[radix] - 1;
        long value = 0;
        for (int pos = 0; pos < s.length(); pos++) {
            int digit = Character.digit(s.charAt(pos), radix);
            if (digit == -1) {
                throw new NumberFormatException(s);
            }
            if (pos > max_safe_pos && overflowInParse(value, digit, radix)) {
                throw new NumberFormatException("Too large for unsigned long: " + s);
            }
            value = (value * radix) + digit;
        }

        return value;
    }

    /**
     * Returns true if (current * radix) + digit is a number too large to be represented by an
     * unsigned long. This is useful for detecting overflow while parsing a string representation of
     * a number. Does not verify whether supplied radix is valid, passing an invalid radix will give
     * undefined results or an ArrayIndexOutOfBoundsException.
     */
    private static boolean overflowInParse(long current, int digit, int radix) {
        if (current >= 0) {
            if (current < maxValueDivs[radix]) {
                return false;
            }
            if (current > maxValueDivs[radix]) {
                return true;
            }
            // current == maxValueDivs[radix]
            return (digit > maxValueMods[radix]);
        }

        // current < 0: high bit is set
        return true;
    }

    /**
     * Returns a string representation of x, where x is treated as unsigned.
     */
    public static String toString(long x) {
        return toString(x, 10);
    }

    /**
     * Returns a string representation of {@code x} for the given radix, where {@code x} is treated
     * as unsigned.
     *
     * @param x the value to convert to a string.
     * @param radix the radix to use while working with {@code x}
     * @throws IllegalArgumentException if {@code radix} is not between {@link Character#MIN_RADIX}
     *         and {@link Character#MAX_RADIX}.
     */
    public static String toString(long x, int radix) {
        if ((radix >= Character.MIN_RADIX && radix <= Character.MAX_RADIX) == false) throw new IllegalArgumentException("radix (%s) must be between Character.MIN_RADIX and Character.MAX_RADIX");

        if (x == 0) {
            // Simply return "0"
            return "0";
        } else {
            char[] buf = new char[64];
            int i = buf.length;
            if (x < 0) {
                // Separate off the last digit using unsigned division. That will leave
                // a number that is nonnegative as a signed integer.
                long quotient = divide(x, radix);
                long rem = x - quotient * radix;
                buf[--i] = Character.forDigit((int) rem, radix);
                x = quotient;
            }
            // Simple modulo/division approach
            while (x > 0) {
                buf[--i] = Character.forDigit((int) (x % radix), radix);
                x /= radix;
            }
            // Generate string
            return new String(buf, i, buf.length - i);
        }
    }

    // calculated as 0xffffffffffffffff / radix
    private static final long[] maxValueDivs = new long[Character.MAX_RADIX + 1];
    private static final int[] maxValueMods = new int[Character.MAX_RADIX + 1];
    private static final int[] maxSafeDigits = new int[Character.MAX_RADIX + 1];
    static {
        BigInteger overflow = new BigInteger("10000000000000000", 16);
        for (int i = Character.MIN_RADIX; i <= Character.MAX_RADIX; i++) {
            maxValueDivs[i] = divide(MAX_VALUE, i);
            maxValueMods[i] = (int) remainder(MAX_VALUE, i);
            maxSafeDigits[i] = overflow.toString(i).length() - 1;
        }
    }
}
